Slotted array antennas often use a waveguide distribution network for distributing RF energy to and from an array of slots placed along the broad wall of a waveguide channel. These waveguide-implemented antennas can be used for communication applications requiring low profile and space-limited mountings, such as aircraft installations. The design of a low profile, space-limited slotted array antenna, however, can be a challenging objective for satellite communication applications, which typically rely upon the transmission and reception of information with two different characteristic polarization states.
A pair of separate spaced-apart antennas, each having a corresponding polarization state, can be used to receive information from a source transmitting information with two different characteristic polarization states. This use of a pair of different antennas, however, often fails to satisfy the need to conserve physical installation space for a space-limited application. Alternatively, a single aperture antenna can be used to receive multiple-polarization information based on the concept of polarization diversity. For example, a dual polarization communications design can be used to reduce an antenna system from two physically separated antennas to a single aperture antenna having two characteristic polarization states.
A prior solution for communicating information with dual characteristic polarization states is an interlaced combination of a pair of slot antennas, a first antenna having slots along the broad wall of a waveguide channel and a second antenna having slots along the narrow wall of a waveguide channel. The slots of the first antenna are associated with a characteristic polarization state, and the slots of the second antenna are associated with another characteristic polarization state. Although the interleaving of separate slot antennas can support the communication of dual polarized information, this antenna design also results in the use of complex end-feed networks and interlaced antennas having different frequency responses. In addition, this stacking of broad and narrow wall waveguide channels in an interleaved manner can be difficult to manufacture for high volume applications. In other words, the interleaving of a pair of broad/narrow wall waveguide antennas to achieve the communication of dual polarized information generally results in increased design activity and a complex manufacturing process.
Another prior dual polarized antenna comprises dual polarized slot radiators in bifurcated waveguide arrays. The radiating element consists of a pair of crossed slots in the sidewall of a bifurcated rectangular waveguide that couples even and odd waveguide modes. One linear polarization is excited by the even mode, and the orthogonal linear polarization is excited by the odd mode. This antenna design approach suffers from the disadvantage of requiring an end-feed network rather than the preferred center or rear-feed network of typical slotted array antennas. In addition, manufacturing the antenna is a relatively complex operation because of the requirement of cutting or stamping out the crossed-slot radiating elements within the wall of the bifurcated rectangular waveguide.
Yet another prior antenna design relies upon a small circular hole or an X-slot located in the broadwall of a rectangular waveguide, approximately half-way between the center line and the narrow wall. A right-hand circular polarization can be achieved by feeding the waveguide from one end. In contrast, a left-hand circular polarization can be achieved by feeding the waveguide from the opposite end. This design suffers from the disadvantage of requiring two separate end-feed networks, rather than the preferred center or rear-feed network of typical slotted array antennas.
Thus, there exists a need for a dual polarized slotted array antenna capable of supporting simultaneous dual polarization states and using a convenient center or rear-feed network. There is also a need for a dual polarized waveguide-implemented antenna employing a planar array of slots, which can be efficiently and readily manufactured using conventional manufacturing techniques. There is also a need for an improved waveguide slot radiator to support the reduction of the profile of a single aperture slotted array antenna capable of supporting simultaneous dual polarization states.